Motor fuel production



Dec. 7, 1943. F. E. FREY MOTOR FUEL PRODUCTION Filed Marh 11, 1940ATTORNEY Patented Dec. 7, 1943 UNITED STATE s ainrrEii'r orricE MOTORFUEL PRODUCTION Frederick'n. Frey,

Delaware Bartlesville, Okla., assigner to Phillips Petroleum Company,

a corporation of Application Maren 11, im,v semina. ses-,in

(ci. 26o-683.4)

` 3 Claims. This invention relates to the production or manufacture ofmotor fuel from low boiling hygranted August 24, 1943, and Serial No.315,063

iiled January 22, 1940, now Patent 2.322,800, granted June 29, 1943.A

Many processes have been proposed for converting normally gaseoushydrocarbons into hydrocarbons having higher molecular weights, such asmotor fuels and lubricants. Some of these processes are dependent uponhaving olefin hydrocarbons present in large proportions in the chargestock, such as in well-known thermal and catalytic polymerizationprocesses'for producing motor fuel from refinery gases containingunsaturated components from cracking stills. Still other processes areadapted to produce motor fuel from normally gaseous paralns, such asunitary` thermal conversion processes, or multistage processes employinga dehydrogenation step as a first part of the process, followed by aconversion of olens so produced. Still other processes have beenproposed wherein a paraiiinic hydrocarbon stream and an oleiinichydrocarbon stream are charged to a process, and the paramns and olensare caused to interreact, or as it is generally stated, the parans arealkylated by the oleiins to form paraftlns having higher molecularweights.

As disclosed in my abovementioned copendingl application Serial No.315,063, now Patent No. 2,322,800, I have found that concentratedhydrofluoric acid will act as a catalyst to eiect a union of unsaturatedhydrocarbons, such as olefins, with parafiins to form higher boilingpar- 'atiin hydrocarbons. I have also found that concentratedhydrofluoric acid can be used as the sole alkylating catalyst, withoutthe presence of such other materials as iinely divided metals, metalhalides, and the like, and that it is preffraction in the presence ofhydroiluoric. acid to f f charged to erable to use as a catalystsubstantially anhydrous hydroiiuoric acid, or hydrogen iuoride.

` l'. have now found that when low boiling pari ains such as butane orpentane are reacted in the presence of concentrated hydro'uoric acidwith certain higher boiling olens, especially those formed by thepolymerization of simpler lower fboiling olei-lns, a parainic productresults which, although higher boiling than the original paraiiin, isnot necessarily higher-boiling than the like, solid high boiling olennreacted, and in fact may at times be lower boiling than the olefin. ThusI have found that when between about 10 and presence of concentratedhydrofluoric acid with an olefin material such as triisobutyiene,boiling between about 345 and 355 F., a paraiiinic p'roduct results ofwhich the predominant part boils between 200 and 240 F. and whichappears to contain large portions of isomeric octanes. Similarly,isooctenes will react with such a butane produce a paraiiinic productcontaining large portions of isooctanes.

The process Aof one modification of the present invention involves acooperation between a polymerization step, for the production of motorfuel range hydrocarbons by the polymerization of lighterl oleiins, andan alkylation step, for the production of motor fuel range hydrocarbonsby the alkylation of lighter parafilns with oleiins which may be heavierland/or lighter than the final product. The polymerization step ispreferably one carried out with the aid of a solid polymerizationcatalyst, such as silica-alumina or the phosphoric acid, acid copperphosphate, or the like; and the alkylation step is carried outl in thepresence of concentrated hydroiluoric acid, using olenns which have beenrecovered #21pm-the eliiuent of the polymerization step. .It husasenfound that the paramns the aikyiation step may be either isoparafns ornormal paraillns, but preferably the parafiinic material should containappreciable portions of isoparaiins such as isobutane (2- methylpropane) or isopentane (Z-methyl butano) or the like, and such may beseparated from'the v forming propanev and isobutene, and hydrogenandmethane are removed from the eiiiuent. A

fraction consisting of hydrocarbons having three and more carbon atomsper molecule and comprising predominantly propene,v isobutene and,isobutane is passed at an elevated pressure over a solid polymerizationcatalyst under conditions such that essentially all of the isobutene ispolymerlzed along with a substantial portion of the propene, formingpolymers in the. gasoline boiling range. Under optimum conditions,consida butane fraction, boiling y 35 F., is reacted in the Atainshigher boiling olenic polymers and some unreacted propone. In thisparticular case the material which is lower boiling than isobutanecontains a large portion of propene and is readily separated from thepolymerization eiliuent by fractional distillation in a depropanizer.Likewise, the higher boiling olenlc polymers are readily separated fromthe gasoline range polymers. Either, or both, of these olenic fractionsconstitute a valuable part of the charge to the alkylation step. In thisparticular instance the unreacted parafilns in the polymerization efuentare predominantly isobutane, and a portion of such a fraction mayconstitute the parainic portion of the hydrocarbon charge to thealkylation step. This fraction will contain a small amount of unreactedisobutene which will' also undergo a desirable reaction in tl'zealkylation step. Isopentane may be blended with the isobutane fractionhargedto the alkylation step or may con.- stitute the entireisoparailinic portion of the charge, or isobutane from some other sourcemay be charged to the alkylation step. Even when higher boiling oleilnicpolymers are the sole olefinic charge to the alkylation, the alkylationproducts will be isoparains in the gasoline boiling range, since itappears that such high boiling polymers undergo concomitant scissionreactions, substantially all of the fragments being oleflnic and takingpart in the reaction, rather than that these higher boiling olefins joindirectly to the charged isoparafiin to form still higher boilingproducts. The gasoline boiling range isoparafilns have highantidetonating qualities land octane numbers, and the olefin polymers inthe gasoline boiling range are also superior in these respects. Thesegasoline products may be used separately as motor fuels or blendingstocks, the olen polymer may be hydrogenated before use; or thesefractions may be blended together to form a premium motor fuel. In thosecases where an oleflnic motor fuel is not undesirable, this latterprocedure is especially effective, since the olens have blending octanenumbers even higherthan their straight octane numbers in the pure state,and to blend them with isoparaillns gives a still more superior result.l

' While the catalystic polymerization produces a polymer which has asuperior octane number, both as it is and after hydrogenation to form aparaillnic material, it fails to convert all of the oleflns charged andgenerally also produces a certain amount of polymer which may beundesirably heavy. Although catalytic alkylation of hydrocarbon materialto` give a product inthe same boiling range produces a paraiilnicproduct directly which also hasl a superior octane number, the octanenumber will generally not be quite as high as that of the formerlproduct resulting from polymerization.

The cooperative combination of the present invention not only gives atotal product with a high' octane number, but also depletes the olencontent of the hydrocarbon stream produced by dehydrogenationand'charged to the alkylation step, and thus aids in producing adesirable alkymer byraising the ratio of parailin to olen in this streamand facilitates control of this reaction. Thus, the combination gives atotal product having an octane number higher than could vbe produced byalkylation alone, andalso results in a better utilization of olefinhydrocarin the gasoline range than would result from catalyticpolymerization alone.

more dilute concentrations may be used, I prefer to use it inconcentrations greater than per cent by weight, the othermaterial beingwater, and I have found that substantially per cent hydroiluoric acid,that is, substantially or completely anhydrous hydrofluoric aoid, orhydrogen fluoride, is very effective, and is particularly adapted to theprocess arrangements to be hereinafter described more fully.. As will bediscussed, the process is generally carried out with the hydrocarbonmaterial substantially in liquid phase; eiilcient reaction -results whensuillcient hydroiluoric acid is employed to result in a substantialsaturation of the liquid hydrocarbon material with hydrogen fluoride,and preferably sufiicient hydrogen iiuoride is used to form a separateliquidv phase which may be maintained emulsifledor intimately mixed withthe hydrocarbon while reaction takes place. In most cases the hydrouoricacid charge should be at least 10 per cent o'f the-total charge, on aliquid volume basis, and hardly ever need exceed 50 or 60 per cent,though more can, at times, be used. In the concentratecll form,hydrofiuoric acid is substantially inert, or non-corrosive, towardnumerous metals; such as copper, nickel, most steels, and various otheralloys which can be used in the constructionof plant equipment.'Occasionalv fortuitous jfreactions may produce minor amounts of-`inorganic fiuorides but, as previously discussed, insofarffas thisinvention is concerned hydroiluoric acid is considered to be used in thesubstantial Aabsence of added metals or metal halides. The .reactiontemperature may be varied over a widerange forany particular re actionmixture,butappears to be most -dependent upon the paraflln hydrocarbonparticiptating in the reaction. Thus, in general, I may carry out analkylation process at temperatures between about 0 and 300 or 400 F. Forreadily reacted parailin hydrocarbons, such as isobutane or isopentane,Imay readily effect an alkylation at a temperature between about 35 and100 F., while for less reactive paramns, such as normal parailins,higher` temperatures of the order of to 300 or 500 F. are necessary ormore desirable.' Theuse-of hydrofiuoric acid has a distinct advantageinsuch cases, in that it can be used under these more extreme' conditionswithout promoting or entering into extensive undesirable side reactions.

As just''men'tioned, higher temperaturesl are necessaryifrigthealkylation of normal paramns, and they .nittyl be caused to react withole'ns in the presence. of' concentrated hydroiiuoric acid attemperatures above about 10o to 120 v ,.pref.,

erably withinathe range of 150 to 300 F., but in ried out lunder onlyslight superatmospheric presf sures, itis preferable to operate undersubstantial superatmospheric pressures, such as about I g n ',100toi,000or2,000poundspersquareinehor more. The process is preferablyconducted with at least an appreciable portion of the reactant materialin liquid phase, although this is not necessary for all reactants.- Whenthe process is conducted with a substantial portion 4of the vreactantsin liquid phase, the reaction temperature should not be above thecritical temperature of the highest boiling reactant, and the pressureshould be at least no less than the vapor pressure ofthis reactant, andpreferably should be at least 500 pounds per square inch. Since thealkylation temperatures, even in the -upper part of the range indicated,are still rather'modcrate, the pressures ordinarily need not beexcessively above the vapor pressure of the reacting mixture and can, ofcourse, be as low ascan be shown by trial to permit effectivealkylation. In many instances normal paraflins can be alkylated in thepresence of hydroiiuorlc acid at pressures between 50 and 500 pounds persquare inch. With some of the lower boiling and less reactive f of theparailins, it may be desirable to conduct the alkvlation at atemperature in the upper part of the range indicated and such that thereactants are predominantly in gaseous phase, even under substantialelevated pressures.'

It is an object of my invention to react normally liquid unsaturatedhydrocarbons with low boiling paraiin hydrocarbons to form paraffinhydrocarbons in the'motor fuel boiling range.

Another object of my invention is to react polymeric oleflns with lowboiling paraflns in the presence of' concentrated hydroiluoric acid toform paraffin hydrocarbons boiling in the motor fuel range.

A further object of my invention is -to provide a process for theproduction of hydrocarbons boiling in the motorfuel range from lowboiling hydrocarbonsby a combination of an olen polymerization step andan olefin-paraffin alkylation step conducted in the presence ofconcentratedA hydrouoric acid.

A still further object of this invention is to react polymeric olensboiling in or above the motor fuel range with low boiling parafiins,especially low boiling isoparains, in the presence of concentrated oranhydrous hydrouoric acid to form parafiin hydrocarbonsboiling near orbelow such as a butane fraction of natural gas containing a highconcentration of isobutane, enters the system through pipe I and valve-I I and is passed by pump I2 through the coil I3 in the dehydrogenatingfurnace I4. In many cases where such a hydrocarbon stream comes directlyvfrom a fractional distillation process or from some other separationstep it may be under a pressure suiliciently high' to obviate thenecessity of the pump I2 and in such a case, of course, the pump may beomitted. The dehydrogenation which takes place in the unit representedby the coil I3 and the furnace I4 may be any type of dehydrogenati'onprocess known to the artand may* be either thermal or catalytic or acombination of both. The pressure will generally not be in excess ofabout 200 pounds per square inch,, and prefer-l gen and any ughtnvamcarbons formed in che dehydrogenation are removed from the systemthrough pipe 23V and valve 2l; and any heavy' hydrocarbons, tar and/orcarbon may be removed from the system through pipe 25 and lvalve 26.This separation may be aided by the use of cooled, unreactedhydrocarbons, (which may be flashed to provide direct vaporization andrefrigeration as has been more fully described by Hays et at. in theircopending application 'Serial No. 336,250, filed May 20, 1940),introduced through pipe 19 and expansion valve 80. A hydrocarbon stream,-comprising unreacted paraiiins and oleiins produced by thedehydrogenation, passes from the separating means 20 through pipe 21 andvalve 28, and is passed at a suitable` polymerization pressure,preferably between 200 and 2000 -pounds per square inch, by

`pump 29 through pipe 30, heater 3I and pipe 32 to the polymerizationunit 33. Normally gaseous unsaturated hydrocarbons, such' as propyleneand/or butenes as may be recovered from an oil cracking process, may beintroduced through pipe 34 and valve 35, and such a stream mayconstitute the only hydrocarbon material charged to this part of theprocess. In such a case the dehydrogenation part of the system justdescribed may not be used, or may be used only to dehydrogenate parainhydrocarbons in the stream .entering through pipe 34 `which pass throughthe polymerization system and are ultimatelypassed. through pipe 63 tothe pipe I0. The polymerization carried out Vin unit 33 will preferablybe a catalytic polymerization rather than a thermal one and may becarried out with any known polymerization catalyst which promotes-theformation of simple, low boiling polymers from light clef-ins such aspropylene and/or butylenes. Such' catalysts may be silica-alumina, solidphosphoric acid, diluted aqueous solutions of liquid acids such assulfuric acid, or the like. If the hydrocarbon stream charged to thispolymerization step contains two or more species of olens such as themixture of propylene and isobutene which results from the thermaldehydrogenation of isobutane, the unit may be so operated as to secureinterpolymerization of these oleflns, one such method being described inFreys copending application Serial No. 294,377, i'lled September 11,1939.

The polymerization eilluent passes through pipe 31 and `valve 38 toseparating means represented' by the fractionating column 40, suppliedwith la heating coil 4I at the bottom and a cooling coil 42 at the top.The entire polymer fraction, comprising olen polymers boiling in themotor fuel range and also higher boiling polymers, passes from thebottom of means 40 through pipe 43 and valve 44 to fractionating column45, wherein a separation is made bef tween light polymers suitable formotor fuel or as a motor fuel blending stock wh'ich is removed from thesystem` through pipe I6 andv valve 41, and heavier polymers which may beremoved through pipe 48 and valve 49. Extremely heavy .polymers or tarand the'like may bev removed 4- assapou from the system through'pipe 50and valve 5|. Separation and fractionation -in the column 45 is aided byheating coil 52 in the bottom and cooling coil 52 in the top.

Light hydrocarbons which havev passed through the polymerization stepunailected, including paraflinhydrocarbons along with unreacted oleiins,pass from the means 40 throughrplpe 55 and valve 58 to the Iractionator60, wherein a separation is made between unreacted hydrocarbons andheavier unreacted hydrocarbons, the separation being aided by a heatingmeans Bifand cooling means 82. Heavier unreacted hydrocarbons, whichwill be substantially entirely paraiilns, pass from the bottom oifractionator 60 through pipe 0 3 controlled by a valve 84, andv may bepassed through valve 05 to pipe i0 and the dehydrogenation step, or anypart or all of this stream may be withdrawn from the system through pipe66 and valve 81. A stream of light unreacted hydrocarbons, which willcontain the majority of the unreacted oleilns, is removed from the topof fractionator 60 through pipe 10, and part vor all of the stream maybe removed through valve 1| when it is not possible or desirable to takecare of this stream by the methods to be hereinafter described, or whenthe content of parafiins is sufhciently high to warrant a discard of apart of this stream or to warrant a separation of paraillns from oleins`in apparatus not shown, .with subsequent reintroduction tothe process ofeither one or both of these fractions as will be readily appreciated. Aportion of the oleiin-containing stream passing through pipe may bediverted through pipe 12 and valve 13 `and returned t0 thepolymerization stepby pump 14.` This may be done by addition of this stream through pipe 15, and valve 16 directly to pipe.r30, or by passing apart or all of the stream through pipe 11, cooler 18, pipe 19 and valve80 as a refrigerat- 'aues or in the motor mei range.

When the polymerization is so conducted that substantially all'the lightoleilns charged are polymerized, the only olens unsuitable for motorfuel will have high molecular weights,l but generally, thepolymerization conditions will not be so drastic'and both light andheavy olens can be sent to the alkylaton step and reacted there,

. and a'process involving this modification is also a part of myinvention.

Heavy oleiins are passed from pipe 48 through pump |08, pipe |'0| andvalve |02 to the alkylation process,- and light olens are passed ingagent to the top of the*fractionato'r4 20, as

previously mentioned. Alternatively, or concomitantly, a portion of thestreampassing through pipe 10 may be passed through-pipe 85 and valve 06to the hydrofluoric acid alkylation step to be more fully hereinafterdiscussedy.. When the dominantly paraffin hydrocarbons such as bu- :l

tanes, while the stream passinglirom this fractionator through pipe 10will coritainfthe major part of the unpolymerized "olens, Ymainlypropene, at least a part, of wlriiclrcan conveniently be recycled to thepolymerization] step. If the polymerization step has beenso conductedthat practically all of the olefin material charged has undergonepolymerization, the stream passing through pipe may be passedVv directlyto pipe 63 through pipe 58 and valve v58, with suitable control ofvalves 56 and 84. g Y

As has been previously discussedpit is an object of this invention toreact olens, which are present in the polymerization eiiluent and whichare unsuitable' by reason of their boiling range or molecular weight fordirect inclusion in motor fuel, with low boiling paramns and especiallylow -boiling isoparafilns in the presence ofl a concencharge to thepolymerizationgstcpcontains apfrom pipe through pump |03, pipe |04 andvalve |05 to thejalkylation process. A suitable hydrocarbon stream, suchas one consisting of or comprising large quantities ci isoparailins suchas isobutane and/or pentane is passed through pump |01 and pipe |08 tothe alkylation process. The paratln hydrocarbons in the etlluent of. thepolymerization step may comprise 'or consist of a portion of the streampassing through pipe 53, which is passed through pipe ||0 and valve topump |01. II such is not the case, or if additional paraffin charge isneeded, paramns may be introduced through pipe H2 and valve ||2 intopipe ||0. Light olens separated from the stream discharged through valve1I and in. a more concentrated form may also be introduced through pipe||2, or through pipe 81 and valve 88 into pipe 85. Polymeric olens fromsome suitable outside source may also be introduced'to the processthrough pipe 81 or ||2, and may at times constitute the sole olen chargeto the process.

Hydroiluoric acid is charged to the process through pipe'ii5, valve lli,pump ||1 and pipe ||8, which in this case leads into pipe |08. .As

one method of performing the alkylation, the' paranlns, olensandhydrofluoric acid may be rapidly and intimately mixed 'at the junctureof pipes |08 and ||8, and the mixture is rapidly passed through the tubecoil |20 in the reactorheat-exchanger |2|. Since the'alkylation reactionis exothermic, it is preferable that this initial part of the reactionshould be carried out withv a removal of heat suicient to maintain adesired operating temperature. A tube coil of a type similar to thatusedv in tube stills eiects' a turbulent mixing of the material passingthrough it, and thus contributes to the emciency of the alkylationreaction. This reaction may be continued and completed in an enlargedchamber |22, which may be insulated and which affords an extendedreaction time` to the mixture with-- out much mixing or turbulence. Itmay at times be desirable to have a part or all or the light olen'senter the alkylation system at some intermediate point or points, and insuch an event this may be accomplished bypassing any desired portion ofthe stream from pipe |00 through one or more pipes illustrated by pipeIIS, controlled by a value |28, to one or more intermediate 'points ofthe coil |20, with suitable control of The hydrocarbon material,containing the hydrocarbons is removed from the top of the separator|24, either as a liquid or as a vapor,

through pipe |30 and valve |3|. It will gener- 'I ally be desirable toeiect an intimate contact of this hydrocarbon material with`- anacidneutralizingl agent such as sodiuml hydroxide or carbonate or thelike, and such material as an aqueous solution or a slurry in somehydrocarbon-miscible material can be introduced through pipe |32 'andvalve |33 and the combined mixture passed to separator |34. Any excessneutralizing agent and products of the neutralization are removed, asthrough pipe |35 and valve |33, while hydrocarbon material is passedthrough pipe |31, valve` I 38, and through pump |36 to hydrocarbonseparating. means illustrated by the fractionator |40 which is equippedwith a heating coil |4| at the bottom and a cooling coil |42 at the top.A hydrocarbon fraction comprising a large proportion of hydrocarbons linthe motor fuel boiling range produced by the alkylation, or in otherwords the alkymer fraction, is removed from a low point of thefractionator |40 through pipe'l43 and valve |44, and may be useddirectly as a premium motor fuel; or it may be used as a blending stock,or maybe subjected to further' fractionation to recover certain narrowboiling fractions of simple composition comprising certain highlydesirable individual hydrocarbons. Heavier hydrocarbons are removed froma lower point of the fractionator through pipe |45 and may be dischargedfrom the system through valve |46. This fraction may at times contain anappreciablev proportion of higher boiling olefin polymers, suitable forreaction in the alkylation step. In such cases, a portion of the streammay be passed from pipe |45 through pipe |41 and valve |48 to pipe 48,where it is mixed with the heavy polymer passing from the polymerizationstep to the alkylation step.

A hydrocarbon steam lighter than the alkymer, and comprising low-boilingunreacted paramns, is removed from an upper part of the fractionator |40through pipe |50, and may be passed through valve |I, pump |52 and pipe|53 to pipe v H0 for further passage through the alkylation stem. Aportion or all of this stream may be passed to the dehydrogenation stepby being passed from pipe |50 through pipe |55 and valve i56 to pipe i0.If desired, this stream may be discharged from the system throughv pipe|51 land valve |58. Any light hydrocarbons which it may be passed fromthis pipe through pipe 90 and valve to pipe |50 and is passed by pump|52 to the alkylation step.

` When isopentane is a. part of the'hydrocarbon material charged to thealkylation step and is present in excess so that an appreciable portionpasses through this step unreacted, a part or all of this unreactedisopentane may be retained lin the'fallqrmer fraction removed throughpipe |43, and at times a part may also be recycledto this step throughpipe |50,pump |52 and pipe |63 and H0, as is readily understood.`:isopentane -asaaoos V 5 produca or the alkylation along with unreactedin itself is va valuable ingredient of premiiimfnoto: fuels. m'introduction 'to une Aaumenta step thus producesa'fuel'having adesirably wide boiling range. and` having a good volatility. Acombination motor fuel having a bightantiknock rating may be formed byblending thematerial produced in the polymerization step witlrthe fueldischarged from the alkylation step. This may I be accomplished bypassing all or any part ofthe fuel flowing through pipe-46, through pipe|65 and valve |66, and mixing it with a stream withdrawn from pipeI43'through pipe |61 and valve |68, with suitable control of valves 41and |44. Both these streams comprise motor fuel hydrocarbons `havinghigh antiknock qualities, and since one, the alkyner, is paraiilnic andthe other. the polymer, is olenic, the resultant blend will be quitehigh as to antiknock value or octane number, since the blending octanenumber of the oleiinic component when blended with a parailinic stock,is not infrequently much higher than the octane number of the oleniccomponent by itself.

' Example I sure of about 1500 pounds per square inch and` at atemperature of about 350 F. The silicaalumina catalyst was prepared bytreating a hydrous silicagel with an aluminum sulfate solution, wherebyalumina was adsorbed, and

washing and drying the resultant material, as described in U. S. Patent2,142,324. vThe reaction time of the polymerization was such that aboutpercent of the olens in the charge were polymerized, forming an olenicpolymer of which over 80 percent boiled below 360 F.

From this olenic polymer a fraction `was separated, by fractionaldistillation, which -boiled between 345 and 355 F., and which consistedessentially of dodecenes. of a liquid butane fraction from natural gas,containing a predominant portion of isobutane, were mixed with about onevolume of substantially anhydrous liquid hydrouoric acid and tothemixture was added about 0.76 volume of the above described polymerfraction. The mixture was vigorously agitated and maintained under apressure between 45 and 55 pounds per square inch gauge. and the olefinfraction was added during.

Boiling` A Refrac- Weight Per pproximate Denrange, tive index per centcent F. @mma mty at 68 F. of total unsat.

Sis-167-.- 1. 3689 4. 2 o. oo 167-203.. 1. 3841 5. 8 0. 10 203-257- 1.3951 61. 6 0. 05 257-306.. CnHzo.. O. 7183 1. 4065 5. 8 0. 05 306-365--CIDH and Cul-124- 0. 7445 1. 4219 12. 7 0. 36 365..- CNH and heavier 0.7670 l. 4312 9. 9 0. 60

About three volumes It is of considerable interest to note that thepredominant fraction of the total product was a mixture of octanes,formed by the general reaction clearly understood at this time, butwhich also appear to produce paraillnic products. Well over 90 percentof the total product was in the present day gasoline boiling range, andpossessed good motor fuel properties.

Example II As an example of the operation of another modification of myinvention, 'a hydrocarbon stream containing about 95 percent isobutanewas thermally dehydrogenated by being passed through a tube coilmaintained at a temperature between 1100 and 1220 F., and under an inletpressure of about 150 pounds per square inch gage, for a period of timesulcient to produce an eiiluent stream containing about 20 mol percentof gaseous oleilns which were about half isobutene and half lighteroleilns predominantly propene.- All but a negligible fraction of thematerial lower boiling than propene was `removed Ffrom thisdehydrogenation eiiiuent, a portion of unreacted propene was added as arecycle stock,

andthe mixture was passed under a pressure of about 1410 pounds persquare inch over a granular silica-alumina catalyst at a temperaturebetween 300 and 475 F. for a period sufficient to convert over 90percent of the isobutene in the charge to polymers; about 50 percent ofthe total propene in the charge also entered into the reaction producingsome interpolymers such as isoheptenes with the isobutene. The normallyliquid hydrocarbons, that is, the polymer fraction, were readilyseparated from the butanes and lighter portion of the effluent.v Aboutone-third of this polymer had more than eight carbon atoms per molecule,and about one-eighthof it was too heavy to be included in a motor fuelhaving 'an end-point of 400 F. The normally gaseous fraction separatedfrom the polymers consisted of Cz and C4 hydrocarbons, which werereadily separated by fractionation into a saturated part containing`about 2 percent olefins and over 95 Apercent isobutane, and anunsaturated partcontaning about 40 p ercent propene. A portion of thislatter fraction was returned to the polymerization step as recyclestock.

The polymer material was separated by fractionation into two parts, oneboiling below about 360 F.A constituting about 82 percent of the totalpolymer. 'I'his material, after being saturated by non-destructivehydrogenation, is a premium blending stock for aviation fuel, having anoctane number of about 91 and a high response tothe addition of anantiknock agent such as tetraethyl lead. The second portion containedthe Ahigher boiling polymers and, although a substantial portion wouldhave been included in a gasoline having a higher endpoint, such as about400 F., such a fraction is considered as a higher-boiling polymerfraction for the purpose o`f thi speciilcation.

This liquid higher-boiling polymer lfraction is blended withapproximately an equal liquid volume of the light unsaturated, unreactedhydrocarbons mentioned above, and the combined stream is mixed withabout 4 liquid volumes of the above mentioned isobutene fraction. 'I'hecombined hydrocarbon stream, as a liquid, is continuously and intimatelymixed with concentrat- ,ed hydroiiuoric vacid of a strength greater thanpercent in a ratio of about 2:1 and is passed through a tube coil at avelocity sufficient to insure turbulent flow. The tube coil is immersedin a bath to regulate the temperature and keep it below F., and is ofsulcient length that the reaction time is about 40 minutes. The eiiiuentis passed as a liquid to a separator, wherein a separation takes placebetween the heavier liquid hydroiiuoric acid and the hydrocarbonmaterial. The hydroiluoric acid is removed and returned to the inlet ofthe tube coil. The hydrocarbon fraction is neutralized by being passedover soda ash, and from ita liquidy product is separated, boilingbelow400 F. andf'constituting about 95 percent of the total normally liquidproduct. It is over 98 percent saturated, contains a large proportion ofisoparafilns, has an initial octane number ofnearly 90 and has anexcellent response to the addition of tetraethyl lead.

As previously mentioned the dehydrogenation step should be conducted ata pressure below about 200 pounds per square inch and "may be eitherthermal or catalytic or a combination of both. Thermal dehydrogenationis preferably carried out between about 1000 and 1250 F., and catalyticdehydrogenation may be carried out between about 850 and 1100 F. In acombination of both, the thermal dehydrogenation should precede thecatalytic. It has been found that the most desirable catalysts compriseorl consist of chromium oxide, preferably the black, unglowed variety.Suitable modications are disclosed in U. S. Patents 1,905,383 and2,098,959, and in the copending applications, Serial Numbers 113,091 ofMorey, (now Patent 2,2t8,320, granted June 30, 19.42) 173,708 ofMatuszak et al., (now Patent 2,294,414, granted September 1, 1942)173,709 of Morey et al., (now Patent 2,312,572, granted March 2, 1943)and 263,000 of Schulze (now Patent 2,291,581, granted July 28, 1942) Thepolymerization step, while it may be thermal or catalytic, is preferablya-catalytic one carried out in the presence of solid granular catalysts.A preferred catalyst is a silica-alumina catalyst, such as described inU. S. Patent 2,142,324 or 2,147,985; or a catalyst of somewhat similarproperties may be prepared by intimately mixing anacidic hydrous silicajelly and hydrous alumina jelly, preferably with the latter beingpresent only to an extent of about 1 to 5' percent by weight,'andsubsequently drying and granulating the resultant material. Asmentioned, other solid catalysts may be used. The pressure willgenerally be at least 200 pounds per square inch and need not be inexcess of ,about` 2000 pounds per square inch. Pressures sufilcient toam a coinventor.

insure a substantially liquid phase operation are the most desirable, asbrought out in the copending application, Serial No. 747,964, now Patnecessary to give a more or less constant or steady polymerization ofthe oleiins.

Many modications and variations of this invention may obviously be used,and can be adapted by one skilled in the art without departing from thespirit of the disclosure. The restriction used in the examples, and inconnection with the drawing, need not necessarily be-used as limi itsfor all particular operations or sets of conditions, since they arepresented primarily as illustrative examples. It will be understood thatthe ilow diagrams presented and described as a part of the disclosureare schematic only, and that many additional conventional pieces ofequipment, such as pressure gauges, valves, pumps, heat exchangers,reflux lines and accumulators, heaters and coolers, and the like,.wi1lbe necessary for any particular installation, and can be supplied tomeet the requirements of any particular case by anyone skilled in theart. The essential equipment and conditions have been described and themodiilcations discussed in sufli Icient detail to serve as efllcientguides..

I claim:

1. A process for the production of premium aliphatic hydrocarbonsboiling in the motor fuel range from isobutane, which comprisesdehydrogenating isobutane to produce isobutene and a moving same fromthe process as a product thereof, separating also a fraction comprisinghigher boiling polymers, a fraction comprising unreacted isobutane, anda fraction comprising unreacted propene, passing through an elongatedreaction zone a stream comprising an intimate liquid mixture oflconcentrated hydrouoric acid and said isobutene fraction and said heavypolymer fraction, removing heat from said mixture in said zone during areaction period to maintain an alkylation temperature, adding at aplurality of points along the length of said reaction zone said propenefraction to supply additional olen reactant to said zone and in amountssuch as -to maintain a relatively low olen concentration, and recoveringfrom an effluent of said zone a hydrocarbon fractioncontalning-paraillns boiling in the motor fuel range so produced.

2. A process for alkylating a low-boiling isoparafiln hydrocarbon offour to ve carbon atoms per molecule to produce isoparaffinsboiling inthe motor fuel range, which comprises passing a stream comprising anintimate, liquid admixture of such an isoparafiin, concentratedhydroiluoric acid and oleiin polymers boiling above the motor fuel rangethrough an elongated reaction zone under alkylating conditions toproduce isoparaffins in the motor fuel range, adding at a plurality ofpoints subsequent to the inlet of and along the length of said reactionzone a normally gaseous oleiln of at least three carbon atoms permolecule to supply additional olefin reactant to said zone and inamounts such as to maintain a relatively low oleiin concentration insaid reaction zone, and recovering from an efuent of said reaction zonea hydrocarbon fraction containing isoparaffins boiling in the motor fuelrange so produced.

3. A process for reacting a low-boiling isoparthe inlet of and along thelength of said reaction zonea normally gaseous oleiln to supplyadditional olefin reactant to said zone and in amoimts such astomaintain a relatively low oleiln concentration in said reaction zone.and recovering from an eilluent of said zone a hydrocarbon fractioncontaining isoparafllns boiling in the motor fuel range so produced.

